This invention relates generally to semiconductor processing and more specifically to improved deposition chambers for the manufacture of semiconductor materials.
The temperature of the walls of a semiconductor reactor (chamber) during operation of the chamber affects, among other things, the efficiency of the process and the quality of the semiconductor wafers produced In the chemical vapor deposition (CVD) process, the substrate (wafer) is heated in a chamber, activating a chemical reaction which deposits a film of material on the surface of the wafer. The walls of the chamber are ideally kept within a narrow temperature range chosen so that unwanted condensation or deposition does not occur on the walls. If the walls or regions of the walls of the chamber are too cold, byproducts of the reaction may condense on the walls or cool regions of the walls. If the walls or regions of the walls of the chamber are too hot, the CVD process may occur on the walls of the chamber or the warmer regions of the walls, as well as on the substrate. Both the cold condensation and hot deposition result in coating of the chamber. This coating must be removed, preferably after each deposition to prevent the coating from flaking off and forming particles on the wafer which degrades wafer quality. The coating is typically removed by an etching process. The need for extensive etching reduces the throughput of the reaction chamber, increasing manufacturing costs. Therefore, it is desired that the coating of the chamber be minimized.
In other semiconductor manufacturing processes, uniformity of the amount of energy reaching the wafer through the walls is an important feature. In the rapid thermal processing (RTP) process, wafers inside the chamber are heated with an energy source located outside the chamber. In the RTP process, uniform temperature distribution at the wafer is important to form a uniform film of the desired material on the substrate. If portions of the chamber walls absorb more or less energy than other portions, the temperature at the wafer will not be uniform, and a nonuniform film will be formed on the wafer.
Methods to maintain the chamber walls near a desired temperature have been reported. U.S. Pat. No. 5,855,677 (Carlson et al.) reports controlling air flow around a reaction chamber in a CVD process to maintain the temperature of the walls of the reaction chamber near a predefined target temperature. U.S. Pat. No. 5,097,890 (Nakao et al.) discloses external cooling of a vertical reaction tube using cooling fluid surrounding the reaction tube.
U.S. Pat. No. 5,129,994 (Ebbing et al.) describes a method of heating one edge of a viewing window by heating a block of a thermally conductive material such as aluminum in contact with the surface of one edge of the viewing window to decrease deposition of polymeric materials on a section of the viewing window.
U.S. Pat. No. 4,653,428 (Wilson et al.) describes a quartz water filter (quartz surfaces surrounding a layer of water) placed between a cold-wall reaction chamber and incident radiation to isolate the substrate from infrared radiation.
Reflectors have also been used around a heating source to generate a more uniform energy distribution (see, for example, U.S. Pat. No. 5,179,677 (Anderson et al.); U.S. Pat. No. 3,862,397 (Anderson et al.); U.S. Pat. No. 4,284,867 (Hill et al.); U.S. Pat. No. 5,062,386 (Christensen); and U.S. Pat. No. 4,794,217 (Quan et al.)).
Coatings have been applied to the inner surface of the reactor to reportedly prevent deposition of by-products. U.S. Pat. No. 5,578,131 (Ye, et al.) reports the use of a layer of halogenated polymeric material with a low sticking coefficient and a low vapor pressure to reduce buildup of byproduct residue on the walls of the chamber. U.S. Pat. No. 5,824,365 (Sandhu, et al.) reports a layer of an electrically insulative metallic oxide on the inner surface of a chamber which reportedly limits adhesion of byproducts of the CVD process on the chamber.
Most chambers have certain locations that experience a higher buildup of coatings than other locations. Also, most chambers have locations where a nonuniform amount of energy is transmitted through the walls. Such local nonuniformity is controllable by localized temperature control. Known methods that modify the temperature of the reaction chamber walls do not permit localized modification. Therefore, methods of locally altering the amount of energy absorbed or wavelengths transmitted by a quartz reaction chamber are needed. Also, the ability to tailor a reaction chamber where the walls are maintained at a selected temperature or selected wavelengths of light are transmitted is needed.
An apparatus for processing substrates comprising a process chamber having walls, said walls having selected regions wherein the temperature is adjusted, whereby the chamber has reduced deposition of byproducts from processing is provided. In one embodiment of the invention, the amount of energy transmitted through the selected regions is adjusted. The amount of energy transmitted through selected regions may be greater or less than the energy transmitted through other regions. In some selected regions, the amount of energy transmitted through the wall may be less than the energy transmitted through other regions of the reaction chamber, and in other selected regions, the amount of energy transmitted may be more than the energy transmitted through other regions of the reaction chamber. Selected regions have at least one characteristic different from other regions of the walls that causes the energy transmission alteration. For example, the selected regions of the walls may have a different concentration of hydroxyl groups than other regions, or may be coated with a material that causes the selected regions to absorb a different amount of energy than other regions. Alternatively, or in combination, the thickness of selected regions of the walls may be a different thickness than in other regions. The temperature of selected regions of the walls may also be modified by positioning one or more energy absorbing elements near the selected regions of the walls. The energy absorbing elements are made of material which is a better absorber of energy than the walls, so that the energy absorbing elements absorb energy and then reradiate energy which is thereafter absorbed by one or more selected wall regions. Alternatively, or in combination, one or more radiation sources are positioned near the selected regions of the walls. The radiation sources emit radiation that is absorbed by selected regions of the chamber. Alternatively, or in combination, reflecting elements are positioned near the selected regions of the walls to reflect energy onto the selected regions of the wall.
All of the various adjusting methods can be employed independently or in combination.
Also provided are methods of minimizing deposition on the walls of a reaction chamber, comprising altering the temperature of one or more selected regions of the walls, whereby deposition on walls during processing of substrates is minimized. The altering step can comprise any one or more of: changing the concentration of hydroxyl groups in selected regions of the walls; increasing or decreasing the thickness of quartz in the selected regions; coating selected regions of the walls with a material that absorbs a different amount of energy than other regions; positioning one or more energy absorbing elements at selected areas around the reaction chamber; positioning a radiation source near a selected area of the chamber, whereby a desired area of the chamber is heated to a greater extent than other areas of the chamber; or positioning a reflecting element at a selected location around the chamber, whereby energy from the chamber is reflected back onto a selected location of the chamber. The reflecting elements are not positioned around the entire chamber.
Also provided is an apparatus having walls, having one or more selected regions in said walls wherein at least one wavelength transmitted through the selected regions is different than the wavelengths transmitted through other regions. xe2x80x9cWavelengthxe2x80x9d includes a selected range of wavelengths. Also provided is a method of making an apparatus having one or more selected regions wherein at least one wavelength transmitted through selected regions is different than the wavelengths transmitted through other regions, comprising one or more of altering the thickness of the quartz in the selected regions so that the desired wavelength is transmitted, altering the composition of the walls (for example, altering the concentration of hydroxyl groups in quartz walls) in the selected regions so that the desired wavelength is transmitted, or coating the selected regions with a material that, in combination with the wall material, transmits the desired wavelength.
Using the methods described herein, selected regions of the chamber may be adjusted to transmit a desired amount of energy. Also, using the methods described herein, the temperature of a selected area of the reaction chamber may be adjusted to match a desired temperature. Using the methods described herein, deposition of selected areas of the chamber may be reduced.
The modifications of the present invention may be in selected regions of the reaction chamber comprising a small total area of the chamber, or may be in larger areas of the chamber. The entire chamber may have more than one selected region. Modifications preferably occur in less than the whole of the chamber, and preferably occur in places that have a greater amount of coating formed during the deposition process. It is not essential that the coatings referred to herein comprise a perfect layer.
The energy that the reaction chamber is exposed to to affect the temperature of the walls may be any source of energy known in the art, including, but not limited to, radiant energy, plasma, and RF fields. The energy may include wavelengths in the range from low ultraviolet to high infrared. Tungsten lamps are preferred for CVD devices.
Other embodiments of the methods and apparatus of this invention and their applications to substrate processing will become apparent from the following figures and description.